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Domestic solar hot water systems use the sun's
energy to heat water in much the same way as water in a hose left lying
on the lawn gets hot on a sunny day. To be effective they do not need
direct sunlight but will receive energy from indirect sunlight (diffuse
radiation), so will work even on a cloudy day. In the UK we get a lot
of diffuse radiation and consequentially receive around 60% of the solar
radiation found at the equator.
In a typical solar hot water system, water is heated as it circulates
through flat, glazed panels or evacuated tubes (solar collectors), located
on the roof of the house. This water is then circulated within a coil
inside your hot water cylinder, so heating the water inside. On days when
there is not enough solar energy, a conventional backup heater provides
the necessary additional energy to heat your water to the desired temperature.
This can be an electric immersion heater or more commonly a gas boiler.
Simplified diagram of a typical solar hot water
system
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